The disclosure relates to non-contacting, gas lubricated seals for rotating components, including but not limited to conditioning and control systems for such seals.
In typical applications, gas lubricated non-contacting seals are disposed to seal a rotating interface between a shaft and housing of a compressor operating to compress a gas. During operation, a portion of the flow of the gas being processed may be diverted from the operating flow and filtered to remove particulate and liquid mist that may be present in the operating flow. This diverted gas flow may be further processed, for example, superheated to a temperature above its dew point, and provided to gas lubricated non-contacting seals as an operating fluid.
Upsets in the compression process, such as improper gas conditioning, or a change in the composition of the operating flow of gas, may cause liquid and/or solid condensates into the diverted gas flow. Such intrusion of liquids and/or solids into a seal interface of the gas lubricated non-contacting seals can lead to reduction of operating life of the seal or, under extreme conditions, failure of the seal.
Non-contacting dry gas seals commonly applied to gas compressors include a seal arrangement (single, tandem, or double), gas conditioning equipment, which is often arranged in modular form, and gas supply controls, which are typically arranged in a control panel. Such combinations are employed for both overhung and beam compressors. Monitoring of seal integrity and operation is typically accomplished by monitoring seal leakage. One can appreciate that a high rate of leakage is used as an indication that the seal has failed, which in the majority of cases is determined after disintegration of the sealing faces requiring an urgent shutting down of the compressor.
Moreover, one requirement for installation of dry gas seals is the ability to accommodate axial movement of the compressor shaft relative to the compressor housing during operation. A typical operating displacement tolerance specification is built into the seal during the design stage. Typically, seal installation plates position the seal at the nominal or optimum position within the compressor housing. The nominal position of an installed seal may be defined by a dimension locating the relationship between the rotating and stationery components that carry the seal components, which is sometimes referred to as the “installation reference” of a seal.
The installation reference dimension is typically measured between a surface that axially determines and secures the axial position of the seal rotor and the seal stator during operation, for example, thrust rings associated with the housing and shaft. Tolerance of axial motion of the seal during operation is needed to accommodate changes in the relative positioning between the rotating and stationary components of the compressor, which the seal components track. Several factors can cause changes in the relative position of a seal, such as the “as-built” condition of the equipment and thermal transients.
The “as-built” condition of a seal is a specific stack-up of tolerances for a given seal arrangement. To address the “as-built” condition, a seal supplier may provide an initial installed tolerance for the seal as installed. Accounting for this condition, a seal may be installed at a “0” position, which still leaves the fall range of the resulting displacement tolerance to accommodate movement within the compressor during operation, the most significant of which typically being thermal transients. As is known, thermal transients can change the relative position of a seal because the compressor rotor may expand or contract at a different rate than the compressor stator or casing due to changes in the temperature of the process fluid, which may result in a dimensional relationship change between the rotor and stator seal components.